Current balancing system for semiconductor elements in parallel

ABSTRACT

A circuit is for balancing currents flowing through a parallel assembly of semiconductor components of the same type. The circuit may include a respective regulation circuit for each semiconductor component. Each regulation circuit may include a comparator of a first signal representative of the current flowing through the component with a reference signal, and a resistive element of a changeable resistance and controlled by the comparator.

This application claims the priority benefit of French Patent application number 14/62572, filed on Dec. 17, 2014, which is hereby incorporated herein in its entirety by reference.

TECHNICAL FIELD

The present disclosure generally relates to electronic circuits, and, more specifically, to a current balancing circuit intended for semiconductor components connected in parallel. The present disclosure more specifically relates to power applications.

BACKGROUND

There exist many applications where a current, which is relatively high as compared with the individual currents that different components are capable of withstanding, is applied to a plurality of semiconductor components of a same type assembled in parallel. Such is the case, in particular, for an assembly of power diodes connected in parallel between two terminals of a′high voltage application (e.g., from tens to hundreds of volts). In the conductive state, each diode sees a current smaller than the total current flowing through the assembly. Ideally, the current seen by each diode, or more generally by each semiconductor element, corresponds to the total current divided by the number of components. In practice, technological dispersions or differences in the manufacturing of semiconductor components, manufacturing tolerances, and/or dispersions due to a temperature differences between each component in the application often cause an imbalance of currents between the different components. This may result in a situation where one of the components conducts a current which exceeds the maximum current that it can withstand.

To overcome this issue, the components may be sorted after manufacturing to only assemble in parallel components having characteristic dispersions which are more limited than manufacturing dispersions. Another approach is to oversize the assembly, that is, to assemble in parallel at least one more component than a number n of components which should be provided to withstand the maximum current of the considered application if all components had identical characteristics. However, these two approaches have a non-negligible cost, which is desirable to avoid.

SUMMARY

In accordance with an example embodiment, a circuit is provided for balancing currents flowing through a parallel assembly of semiconductor components of the same type. The circuit may include, for each component, a regulation circuit including a comparator of a first signal representative of the current flowing through the component with a reference signal, and a resistive element of a settable or changeable resistance, controlled by the comparator.

According to an example embodiment, the reference signal may be representative of the total current flowing through the assembly, divided by the number of components. According to another example aspect, in each regulation circuit, the resistive element of changeable resistance is a MOS transistor.

In accordance with another example aspect, in each regulation circuit, the resistive element of changeable resistance may be series-connected with the component having the regulation circuit associated therewith. Each regulation circuit may include a current measurement resistor to be series-connected with the component having the regulation circuit associated therewith. In each regulation circuit, the first signal may be the voltage across the current measurement resistor.

According to another example aspect, in each regulation circuit, the comparator may include an operational amplifier having a first input receiving the first signal and having a second input receiving the reference signal. The circuit may also include a circuit for providing the reference signal and comprising a circuit for summing the first signals provided by the different regulation circuits, and a circuit for dividing an output signal of the summing circuit by the number of components. In accordance with an example embodiment, the summing circuit may comprise at least one operational amplifier. Furthermore, the dividing circuit may comprise a resistive voltage dividing bridge. Additionally, the regulation circuits may be identical to one another.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a simplified schematic drawing of a parallel association of semiconductor components of the type with which the embodiments described herein may be used;

FIG. 2 is a schematic block diagram of an embodiment of a system for balancing the currents flowing through semiconductor elements assembled in parallel; and

FIG. 3 is a schematic circuit diagram of the system of FIG. 2, illustrating in greater detail an example embodiment of a balancing circuit.

DETAILED DESCRIPTION

For clarity, the same elements have been designated with the same reference numerals in the various drawings. Further, only those elements which are useful to the understanding of the described embodiments have been detailed. In particular, the uses which may be made of a parallel assembly of semiconductor components have not been detailed, the described embodiments being compatible with typical applications using a plurality of semiconductor components of the same type connected in parallel.

FIG. 1 is a simplified representation of an assembly of n semiconductor components D₁, D₂, . . . D_(n), connected in parallel between terminals A and K. Components D_(i) (i being an integer in the range from 1 to n) are identical, for example, to within manufacturing dispersions or tolerances. In operation, during a phase of turning on the assembly, a current I_(T) may flow between terminals A and K. Each component D_(i) then conducts a current I_(Di) smaller than current I_(T). Applications of such parallel assemblies of semiconductor components include protection devices, AC/DC or DC/DC voltage conversion devices such as high voltage and/or high current switched-mode power supplies (applications such as traction motors, solar inverters, welding machines, embarked charger for an electric or hybrid vehicle . . . ), etc. Components D₁ to D_(n) are, for example, semiconductor diodes, but may more generally be semiconductor components of another type, such as MOS transistors, IGBT transistors, switches, Schottky diodes, Zener diodes, etc.

In an assembly of the type in FIG. 1, dispersions or differences between the different components may result in one or a plurality of components conducting a current greater than the maximum current that the component can withstand. FIG. 2 schematically shows an embodiment of a system including a parallel assembly of n semiconductor components D₁ to D_(n), and a circuit 200 for balancing the currents flowing through components D₁ to D_(n). Each component D_(i) includes two main conduction terminals a_(i) and k_(i). In the illustrated example, each component D_(i) is a diode, and terminals a_(i) and k_(i) respectively correspond to the anode and to the cathode of the diode. Components D_(i) are connected in parallel between terminals A and K of the assembly, via their conduction terminals a_(i) and k_(i). In the illustrated example, each component D_(i) has its terminal a_(i) connected to terminal A, and its terminal k₁ is connected to terminal K via a balancing circuit 200.

The balancing circuit 200 illustratively includes n connection terminals b₁ to b_(n) respectively connected to the n terminals k₁ to k_(n) of components D₁ to D_(n). In the illustrated example, terminals b₁ to b_(n) are directly connected to terminals k₁ to k_(n), respectively. The balancing circuit 200 further includes an additional connection terminal c connected to terminal K. In the present example, terminal c is directly connected to terminal K.

A circuit 200 includes n current regulation circuits C_(i) which are, for example, identical or similar. Each circuit C_(i) is associated with the component D_(i) of the same rank i. More specifically, each regulation circuit C_(i) is connected between terminal b_(i) of the same rank i and terminal c of the balancing circuit 200.

In operation, during a conduction phase of the system, a current I_(T) may flow between terminals A and K. Each component D_(i) then conducts a current I_(Di) smaller than current I_(T). Each regulation circuit C_(i) conducts, between its nodes of connection to terminals b_(i) and c, the same current I_(Di) as component D_(i) associated therewith.

Each regulation circuit C_(i) includes a node d_(i) for supplying a signal V_(FBi), representative of current I_(Di) flowing between terminals b_(i) and c. Each regulation circuit C_(i) further illustratively includes a node e_(i) which receives of a reference signal V_(REF), for example, of the same nature as signal V_(FBi). All regulation circuits C_(i) receive the same reference signal V_(REF) on their respective nodes e_(i). Each regulation circuit C_(i) is capable or configured to vary its resistance between terminals b_(i) and c to modify current I_(Di) to minimize the interval between signal V_(FBi) and V_(REF).

Balancing circuit 200 further includes a circuit 202 for providing the reference signal V_(REF). The circuit 202 includes n input nodes respectively connected to nodes d₁ to d_(n) of circuits C₁ to C_(n). The circuit 202 further includes a node for supplying signal V_(REF) and connected to the n nodes e₁ to e_(n) of circuits C₁ to C_(n). The circuit 202 is capable of or configured to supply a signal V_(REF) equal to the sum of the n signals V_(FBi) applied to its input nodes, divided by number n of components D_(i) of the assembly.

Thus, the circuit 200 is capable of or configured to measure, in each branch of the parallel assembly of components D₁ to D_(n), a variable representative of current I_(Di) flowing through the branch, and measure this variable with a variable representative of the total current I_(T) divided by number n of components. It is further configured to accordingly modify the resistance of the branch to balance the different currents I_(Di) of the assembly. The system control results in that, in each branch of the assembly, current I_(Di) of the branch tends, for a balanced system, towards a value I_(T)/n.

FIG. 3 is an electrical circuit diagram of the system of FIG. 2, illustrating in more detailed fashion an embodiment of the balancing circuit 200. In this example, each circuit C_(i) includes, in series between terminal b_(i) and terminal c, an element of settable resistance 301 and a resistive element R_(sense) for measuring current I_(Di). In the illustrated example, element 301 is a MOS transistor having a resistance which may be set by application of a setting voltage on its control gate. As a variation, the element 301 may be a bipolar transistor or any other element having a settable or changeable resistance. In the present description, although resistive elements R_(sense) of the resistors will be taken as an example, these resistors may take different forms, including that of MOS transistors.

In the illustrated example, the element 301 is connected between nodes b_(i) and d_(i) of circuit C_(i), and the element R_(sense) is connected between node d_(i) of circuit C_(i) and terminal c. Thus, in this example, information V_(FBi) provided on node d_(i) of circuit C_(i) is the voltage on node d_(i), or the voltage across resistor R_(sense), which is proportional to the current I_(Di) flowing in the branch including, in series between terminals A and K, component D_(i), settable resistance element 301, and resistive measurement element R_(sense).

In the example of FIG. 3, each circuit C_(i) illustratively includes an operational amplifier 303 assembled as an analog voltage comparator. The amplifier 303 has an inverting input (−) connected to node e_(i) of application of signal V_(REF) via a resistor 305, and a non-inverting input (+) connected to node d_(i) for providing signal V_(FBi) via a resistor 307. A resistor 309 is further connected between the non-inverting input (A) of the amplifier 303 and a node GND of application of a reference potential, e.g., connected to terminal K. Further, a resistor 311 is connected between the inverting input (−) of the amplifier 303 and the output of the amplifier. Resistors 305 and 307, on the one hand, and 309 and 311, on the other hand, preferably have the same values. Thus, amplifier 303 provides an output signal proportional to the difference between voltages V_(FBi) and V_(REF). The output of amplifier 303 is connected to a control node of the transistor 301.

In this example, the MOS transistor 301 operates in a linear mode, that is, the control signal applied to the gate of the transistor 301 varies the on-state series resistance of the transistor 301. The function of the amplifier 303, which is configured as a comparator, r is to apply to the control gate of the transistor 301 a signal tending to increase the resistance of the transistor 301 (and thus decrease current I_(Di)) if the signal V_(FBi) is greater than the reference signal V_(REF), and to decrease the resistance of the transistor 301 (and thus increase the current I_(Di)) if the signal V_(FBi) is smaller than signal V_(REF).

In the example of FIG. 3, the circuit 202 for generating the signal V_(REF) includes a circuit 321 for summing voltages V_(FBi) sampled from nodes d_(i) of circuits C_(i). The circuit 321 supplies, on a node g, a voltage equal to the sum of voltages V_(FBi). The circuit 321 may include one or more operational amplifiers (not shown).

The circuit 202 further includes, between node g and node c, a resistor 323 in series with a resistor 325. The junction point of resistors 323 and 325 is connected to node f for supplying the signal V_(REF).

The resistors 323 and 325 of the circuit 202 form a voltage-dividing bridge. Thus, the voltage V_(REF) provided on the node f of the circuit 202 is equal to the voltage applied to the node g (that is, the sum of voltages V_(FBi)), divided by a coefficient (R₃₂₃+R₃₂₅)/R₃₂₅, where R₃₂₃ and R₃₂₅ respectively designate the value of resistor 323 and the value of resistor 325. In this example, the resistors 323 and 325 are selected to be such that n=(R₃₂₃+R₃₂₅)/R₃₂₅, n being the number of components D_(i) connected to the balancing circuit 200.

As a non-limiting example, the circuit 200 may be made in the form of an integrated circuit on a semiconductor chip including n+1 terminals connected to the parallel assembly of components D_(i) (terminals b₁ to b_(n) and terminal c). As a variation, the elements of the circuit 200 may be integrated on a same semiconductor chip, except for the resistor 325, which may be a discrete resistor external to the integrated circuit. In this case, the semiconductor chip may include n+2 connection terminals (terminals b₁ to b_(n), terminal c, and terminal f). This makes it possible to adjust the value of the resistor 325 according to the given application, particularly if the number of branches of the parallel assembly of components D_(i) is desired to be modified.

An advantage of the embodiment of FIG. 3 is that the cost, the bulk, and the consumption of the balancing circuit 200 are relatively low. In particular, the MOS transistors 301 may be low-voltage transistors. Indeed, in the non-conductive state of the assembly (i.e., when a negative voltage is applied between terminals A and K of the assembly), each transistor 301 is conductive due to the body diode of this transistor. The voltage is thus not withstood by the transistors 301, but by the components D_(i). Further, the power consumption of the transistors 301 of the balancing circuit only occurs in the presence of an imbalance of currents I_(Di). Further, the resistors R_(sense) may be of low value, for example, of a value in the range from 10 to 100 mΩ, and may result in only a relatively small energy dissipation or consumption.

While specific embodiments have been described above, various alterations, modifications, and improvements will readily occur to those skilled in the art. In particular, the described embodiments are not limited to the specific example of the balancing circuit shown in FIG. 3. As a variation, in each regulation circuit C_(i), information V_(FBI) representative of the current I_(Di) flowing through the component D_(i) may be a current, for example, obtained by a current mirror. In this case, the summing performed in the circuit 202 may be a summing of currents and signal V_(REF) may also be a current.

Further, it will be within the abilities of those skilled in the art to adapt the described embodiments to the case where the semiconductor components D_(i) will have nominal characteristics different from one another. In this case, the values of the different resistors may be adapted. In particular, in the example of FIG. 3, the different circuits C_(i) may include one or more of the resistors R_(sense), resistors 305, resistors 307, resistors 309, and/or resistors 311 having different values.

Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and the scope of the present invention. Accordingly, the foregoing description is by way of example only and is not intended to be limiting. 

1-10. (canceled)
 11. A circuit for balancing currents flowing through a parallel-connected assembly of semiconductor components of a same type, the circuit comprising: a respective regulation circuit for each semiconductor component comprising a resistive element having a changeable resistance, and a comparator configured to compare a first signal representative of a current flowing through the respective semiconductor component with a reference signal, and to change the changeable resistance of said resistive element based thereon.
 12. The circuit of claim 11 wherein the reference signal is representative of a total current flowing through the assembly divided by a number of the semiconductor components.
 13. The circuit of claim 11 wherein said resistive element comprises a MOS transistor.
 14. The circuit of claim 11 wherein said resistive element is to be series-connected with its respective semiconductor component.
 15. The circuit of claim 11 wherein each regulation circuit further comprises a current measurement resistor to be series-connected with the respective semiconductor component; and wherein, in each regulation circuit, the first signal is the voltage across the current measurement resistor.
 16. The circuit of claim 11 wherein each comparator comprises an operational amplifier having a first input receiving the first signal and a second input receiving the reference signal.
 17. The circuit of claim 11 further comprising a reference voltage signal generator for generating the reference signal and comprising: a summing circuit configured to sum the first signals from said regulation circuits; and a division circuit configured to divide an output signal of the summing circuit by a number of semiconductor components to generate the reference signal.
 18. The circuit of claim 17 wherein said summing circuit comprises at least one operational amplifier.
 19. The circuit of claim 17 wherein said division circuit comprises a resistive voltage-dividing bridge.
 20. The circuit of claim 11 wherein said regulation circuits are identical to one another.
 21. An electronic device comprising: a plurality of parallel-connected semiconductor components of a same type; and a respective regulation circuit for each semiconductor component comprising a resistive element having a changeable resistance, and a comparator configured to compare a first signal representative of a current flowing through the respective semiconductor component with a reference signal, and to change the changeable resistance of said resistive element based thereon.
 22. The electronic device of claim 21 wherein the reference signal is representative of a total current flowing through the assembly divided by a number of the semiconductor components.
 23. The electronic device of claim 21 wherein each resistive element comprises a MOS transistor.
 24. The electronic device of claim 21 wherein each resistive element is series-connected with its respective semiconductor component.
 25. The electronic device of claim 21 wherein each regulation circuit further comprises a current measurement resistor series-connected with its respective semiconductor component; and wherein, in each regulation circuit, the first signal is the voltage across the current measurement resistor.
 26. The electronic device of claim 21 wherein each comparator comprises an operational amplifier having a first input receiving the first signal and a second input receiving the reference signal.
 27. The electronic device of claim 21 further comprising a reference voltage signal generator for generating the reference signal and comprising: a summing circuit configured to sum the first signals from said regulation circuits; and a division circuit configured to divide an output signal of said summing circuit by the number of semiconductor components to generate the reference signal.
 28. A method for balancing currents flowing through a parallel-connected assembly of semiconductor components of a same type, with a respective resistive element having a changeable resistance coupled to each of the semiconductor components, the method comprising: comparing a first signal representative of a current flowing through the respective semiconductor component with a reference signal; and changing the changeable resistance of the resistive element based upon the comparison.
 29. The method of claim 28 wherein the reference signal is representative of a total current flowing through the assembly divided by a number of the semiconductor components.
 30. The method of claim 28 wherein each resistive element comprises a MOS transistor.
 31. The method of claim 28 wherein each resistive element is series-connected with its respective semiconductor component. 